Can you countersink the strut so that the larger diameter on the stalk recesses into the strut. Looks like there is enough length available meaning the amount you countersink would be equal to the amount that will extend inside the fender. If you're threads are about flush in the inside right now, it looks like you could get about the width of a nut and thin washer out of it.

 

That is a damn good idea! Thank you! Why didn't I think of that?